注:本文应用于 1.13+
效果
实现方式
首先要实现在线时间统计，需要先定义时间。 所以在这里 需要先创建几个稍后要用到的计分板：
/scoreboard objectives add timetick dummy
/scoreboard objectives add times dummy
/scoreboard objectives add timem dummy
/scoreboard objectives add timeh dummy
/scoreboard objectives add timed dummy
顺次显示的是 秒-分-时-天。
计时器的思路是这样的： 使用循环命令方块为 timetick 加分，则每秒可以增加 20（每秒命令方块运行 20 次） 当 timetick 为 20 时，为 times 加 1 并设置 timetick 为 0。 当 times 为 60 时，为 timem 加 1 并设置 times 为 0。 当 timem 为 60 时，为 timeh 加 1 并设置 timem 为 0。 ...以此类推。
所以在这里 需要使用命令方块组+目标选择器进行选择性加分:
循环: scoreboard players add @a timetick 1
连锁: scoreboard players add @a[scores=\{timetick=20..}] times 1
连锁: scoreboard players set @a[scores=\{timetick=20..}] timetick 0
连锁: scoreboard players add @a[scores=\{times=60..}] timem 1
连锁: scoreboard players set @a[scores=\{times=60..}] times 0
连锁: scoreboard players add @a[scores=\{timem=60..}] timeh 1
连锁: scoreboard players set @a[scores=\{timem=60..}] timem 0
连锁: scoreboard players add @a[scores=\{timeh=24..}] timed 1
连锁: scoreboard players set @a[scores=\{timeh=24..}] timeh 0
最后 再加一个 title 用于显示即可
循环： execute as @a at @s run title @p actionbar [\{"text":"在线时间:","color":"green","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false},\{"score":\{"objective":"timed","name":"@p"},"color":"gray","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false},\{"text":"天","color":"gold","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false},\{"score":\{"objective":"timeh","name":"@p"},"color":"gray","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false},\{"text":"小时","color":"gold","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false},\{"score":\{"objective":"timem","name":"@p"},"color":"gray","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false},\{"text":"分","color":"gold","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false},\{"score":\{"objective":"times","name":"@p"},"color":"gray","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false},\{"text":"秒","color":"gold","bold":false,"italic":false,"underlined":false,"strikethrough":false,"obfuscated":false}]
（考虑到多人游戏的情况 这里添加了一个 execute 用于保证显示正确的对象）
当我们搭建好全部命令方块并运行后，不难发现虽然计时器正常，但却没有显示值为 0 的项目:
这是因为未被赋值的计分板项目默认不显示，需要手动设置为 0：
/scoreboard players set @p times 0
/scoreboard players set @p timem 0
/scoreboard players set @p timeh 0
/scoreboard players set @p timed 0
之后即可正常使用。
命令
/scoreboard objectives add timetick dummy
/scoreboard objectives add times dummy
/scoreboard objectives add timem dummy
/scoreboard objectives add timeh dummy
/scoreboard objectives add timed du
/scoreboard players set @p times 0
/scoreboard players set @p timem 0
/scoreboard players set @p timeh 0
/scoreboard players set @p time
循环: scoreboard players add @a timetick 1
连锁: scoreboard players add @a[scores=\{timetick=20..}] times 1
连锁: scoreboard players set @a[scores=\{timetick=20..}] timetick 0
连锁: scoreboard players add @a[scores=\{times=60..}] timem 1
连锁: scoreboard players add @a[scores=\{timem=60..}] timeh 1
连锁: scoreboard players set @a[scores=\{timem=60..}] timem 0
连锁: scoreboard players add @a[scores=\{timeh=24..}] timed 1
连锁: scoreboard players set @a[scores=\{timeh=24..}] timeh 0
循环: execute as @a at @s run title @p actionbar [\{"text":"在线时"color":"green","bold":false,"italic":false,"underlined":fa"strikethrough":false,"obfuscated":false},\{"score":\{"objective":"tim"name":"@p"},"color":"gray","bold":false,"italic":false,"underlined":fa"strikethrough":false,"obfuscated":false},\{"text":"天","color":"go"bold":false,"italic":false,"underlined":false,"strikethrough":fa"obfuscated":false},\{"score":\{"objective":"timeh","name":"@p"},"color":"gr"bold":false,"italic":false,"underlined":false,"strikethrough":fa"obfuscated":false},\{"text":"小时","color":"gold","bold":false,"italic":fa"underlined":false,"strikethrough":false,"obfuscated":false},\{"sco\{"objective":"timem","name":"@p"},"color":"gray","bold":false,"italic":fa"underlined":false,"strikethrough":false,"obfuscated":false},\{"text":"color":"gold","bold":false,"italic":false,"underlined":fa"strikethrough":false,"obfuscated":false},\{"score":\{"objective":"tim"name":"@p"},"color":"gray","bold":false,"italic":false,"underlined":fa"strikethrough":false,"obfuscated":false},\{"text":"秒","color":"go"bold":false,"italic":false,"underlined":false,"strikethrough":fa"obfuscated":false}]
OOC
/summon falling_block ~ ~1.5 ~ \{Time:1,BlockState:\{Name:"minecraft:redstone_block"},Motion:[0d,-1d,0d],Passengers:[\{id:falling_block,Time:1,BlockState:\{Name:"minecraft:activator_rail"},Passengers:[\{id:command_block_minecart,Command:"/data merge block ~ ~-2 ~ \{auto:0b,Command:\"\"}"},\{id:command_block_minecart,Command:"/scoreboard objectives add timetick dummy\n/scoreboard objectives add times dummy\n/scoreboard objectives add timem dummy\n/scoreboard objectives add timeh dummy\n/scoreboard objectives add timed dummy\n/scoreboard players set @p times 0 \n/scoreboard players set @p timem 0 \n/scoreboard players set @p timeh 0 \n/scoreboard players set @p timed 0 \nscoreboard players add @a timetick 1\nscoreboard players add @a[scores=\{timetick=20..}] times 1 \nscoreboard players set @a[scores=\{timetick=20..}] timetick 0 \nscoreboard players add @a[scores=\{times=60..}] timem 1\nscoreboard players add @a[scores=\{timem=60..}] timeh 1 \nscoreboard players set @a[scores=\{timem=60..}] timem 0 \nscoreboard players add @a[scores=\{timeh=24..}] timed 1 \nscoreboard players set @a[scores=\{timeh=24..}] timeh 0 \nexecute as @a at @s run title @p actionbar [\{\"text\":\"在线时间:\",\"color\":\"green\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false},\{\"score\":\{\"objective\":\"timed\",\"name\":\"@p\"},\"color\":\"gray\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false},\{\"text\":\"天\",\"color\":\"gold\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false},\{\"score\":\{\"objective\":\"timeh\",\"name\":\"@p\"},\"color\":\"gray\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false},\{\"text\":\"小时\",\"color\":\"gold\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false},\{\"score\":\{\"objective\":\"timem\",\"name\":\"@p\"},\"color\":\"gray\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false},\{\"text\":\"分\",\"color\":\"gold\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false},\{\"score\":\{\"objective\":\"times\",\"name\":\"@p\"},\"color\":\"gray\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false},\{\"text\":\"秒\",\"color\":\"gold\",\"bold\":false,\"italic\":false,\"underlined\":false,\"strikethrough\":false,\"obfuscated\":false}]"},\{id:command_block_minecart,Command:"setblock ~ ~1 ~ command_block\{auto:1b,Command:\"fill ~ ~ ~ ~ ~-2 ~ air\"} replace"},\{id:command_block_minecart,Command:"kill @e[type=command_block_minecart,distance=..1]"}]}]}
